In typical histological practice, a bulk tissue specimen is processed by treatment with a succession of fluids or vapours to extract its aqueous content so as to allow of its impregnation with wax or resin to provide the specimen with sufficient rigidity to enable thin sections to be cut from it with a microtome. Sections of interest are then mounted on slides or other carriers and, usually, further processed thereon so that they display required characteristics for microscopic examination. For instance, a mounted tissue section may be processed to remove the wax or resin and to accomplish rehydration so that the tissue section is receptive to dyes or other staining agents.
The processing of bulk tissue specimens has been largely automated in modern laboratory practice. Similarly, significant automation of the processing of slide-mounted tissue sections has been achieved in practice. However, whereas the liquids and other reagents used for processing bulk tissue specimens are relatively inexpensive so that processing techniques involving their use in large quantities are acceptable in practice, some of the processing techniques now being applied to slide mounted materials involve the use of reagents that are costly and require to be applied to the material in very small quantities under closely controlled conditions of temperature and duration. The so called "immuno-staining" procedures are cases in point. Existing techniques lack the controllability and/or economy of reagents desirable for such procedures.